1. Field
The present invention relates to a synchronous transmission device and to, for example, a SONET EOS (Ethernet® over SONET) termination device and its peripheral device.
2. Description of the Related Art
An EoS technique is known as a technique for building a complex network. In one such complex network, an Ethernet® network is linked to a Synchronous Optical Network (SONET) network. In another such complex network, an Ethernet network is linked to a Synchronous Digital Hierarchy (SDH) network. Further, a Path Protection technique is employed in a transmission device constituting a SONET network or an SDH network. The Path Protection technique protects communication by switching the paths at the time of a link failure or a device failure. In recent years, a Protection (redundancy) function has been required to be installed for the connection line to an Ethernet® device connected to a SONET network or an SDH network.
FIG. 1 is a diagram showing an exemplary configuration of a packet switch (Packet SW) device applied to an Ethernet® network (referred to as a packet network, hereinafter). The packet switch device includes a plurality of interface cards accommodating a plurality of Ethernet® lines (E-lines, hereinafter). The Ethernet lines are connected to a packet switch. Each interface card and the packet switch are connected through a packet interface such as a System Packet Interface (SPI). The packet switch performs switching operation on a packet basis.
FIG. 2 is a diagram showing an exemplary configuration of a SONET transmission device or an SDH transmission device (generically referred to as a SONET device, hereinafter). As shown in FIG. 2, the SONET device is constructed by connecting a plurality of interface cards accommodating a plurality of lines to a SONET switch. Here, each interface card in the SONET device and the SONET switch are connected through a SONET interface (e.g., the STS12 format). Switching operations are performed in the SONET switch on a time slot basis.
Here, for the purpose of realization of a redundant configuration (Ethernet® Protection) in a packet network, collection and distribution need be performed on a packet basis. Thus, for the purpose of realization of a protection function (redundant configuration) between interface cards in a SONET device, the SONET switch needs to process on a packet basis. Nevertheless, the SONET switch that performs switching operations on a time slot basis cannot perform switching on a packet basis.
Thus, a protection function between interface cards has been difficult to realize in existing SONET devices. Here, the above-mentioned protection function may be realized by installing a packet switch function in the SONET switch. Nevertheless, adding functions by installing a packet switch into an existing SONET switch (existing hardware constructed as a switch card) can cause an increase in the cost or an increase in the power consumption in the SONET device.